1. Field of the Invention
The present invention relates to an anesthetic-depth monitor apparatus which monitors an anesthetic depth of a living subject who is undergoing a surgical operation. The anesthetic depth means a degree of suppression of pain or consciousness of the subject.
2. Related Art Statement
It is desirable that the degree of anesthesia of a patient who is undergoing a surgical operation be not too shallow nor too deep, that is, be kept at an appropriate level. To this end, it has conventionally been practiced to monitor the anesthetic depth of a patient by measuring the change of his or her blood pressure, heart rate, or respiration rate in response to the surgical stimuli, or observing his or her cilium reflex or pupil's diameter, or the color or temperature of his or her limb or peripheral body portion. In addition, U.S. Pat. Nos. 5,871,450 and 5,964,713, assigned to the Assignee of the present application, disclose an anesthetic-depth measuring device which determines an anesthetic depth based on the ratio of peripheral body temperature to deep body temperature, and an anesthetic-depth measuring device which determines an anesthetic depth based on the fluctuations of pulse period or blood pressure.
However, in some cases, the conventional devices may not enjoy the highest reliability. For example, in the case where a conventional device is used to monitor the anesthetic depth of a patient to keep it at an appropriate level, the anesthesia may not be kept sufficiently deep so that the patient may be awaken, which causes the patient to feel much discomfort. To avoid this, it is likely to administer, in an actual surgical operation, too much anesthetic agent to the patient. However, the administration of too much anesthetic agent delays the awakening of the patient after the operation. In addition, the consumption of too much anesthetic agent is not economical.